Scientists said to get DNA-like molecule to assemble itself

Chemists say they have found a way to make a DNA-like mol­e­cule as­sem­ble it­self in a pond-like set­ting—po­ten­tially sug­gest­ing a key step in how life orig­i­nat­ed.

The re­search­ers ac­tu­ally worked with a sim­pler mol­e­cule, called pre-RNA. It’s hy­poth­e­sized to have even­tu­ally evolved in­to DNA—one stop­ping point along the way hav­ing been the crea­t­ion of a third sub­stance, RNA, still used in the body to trans­late the code in­scribed in DNA.

Sci­en­tists had long strug­gled to show how even pre-RNA, the eas­i­est to build of the three mol­e­cules, might have self-as­sem­bled. To­day they don’t need to—they are cop­ied us­ing pre-existing cel­lu­lar machin­ery—but the first ones pre­sumably had no such help.

The study dem­on­strat­ed a chem­i­cal re­ac­tion “that we see as im­por­tant for the forma­t­ion of the ear­li­est RNA-like mol­e­cules,” said one of the re­search­ers, bio­chem­ist Nich­o­las Hud, who di­rects the Cen­ter for Chem­i­cal Ev­o­lu­tion at the Geor­gia In­sti­tute of Tech­nol­o­gy. The study was pub­lished Dec. 14 on­line in the Jour­nal of the Amer­i­can Chem­i­cal So­ci­e­ty.

RNA or pre-RNA con­sist of three chem­i­cals. Two are ri­bose and phos­phate. The third is called a base, but there are a few pos­si­ble bas­es. The three com­po­nents, in any event, link to­geth­er to form just one un­it of the mol­e­cule. The whole mol­e­cule con­sists of many of these un­its. This al­lows it to store in­forma­t­ion, em­bed­ded in the spe­cif­ic se­quence of bas­es. DNA is si­m­i­lar to the oth­er two mol­e­cules, though it’s double-stranded, like a lad­der—good for its sta­bil­ity—whereas the oth­er mol­e­cules are single-stranded, like lad­ders cut down the mid­dle.

Hud’s team in­ves­t­i­gated bas­es chem­ic­ally re­lat­ed to those of mod­ern RNA, but that might be able to spon­ta­ne­ously bond with ri­bose and as­sem­ble with oth­er bas­es. They fo­cused on a mol­e­cule called tri­am­in­opy­rim­i­dine, or TAP, which they mixed with ri­bose un­der con­di­tions meant to mim­ic a dry­ing pond on early Earth.

TAP and ri­bose re­acted to­geth­er with up to 80 per­cent of TAP be­ing con­vert­ed in­to nu­cle­o­sides, the un­its of RNA, the sci­en­tists re­ported. “This study is im­por­tant in show­ing a fea­si­ble step for how we get the start of an RNA-like mol­e­cule,” and al­so how the build­ing blocks “could have found each oth­er and self-as­sem­bled in what would have been a very com­plex mix­ture of chem­i­cals,” Hud said.